Metamaterials May Be Used to Make Objects Invisible

Sir John B. Pendry of Imperial College London and collaborators David R. Smith and David Schurig of Duke University in Durham, N.C., and Ulf Leonhardt of the University of St. Andrews in the UK have independently calculated that metamaterials can be designed to guide electric, magnetic or electromagnetic fields around an object and make it invisible to the outside world. Potential applications of such media include stealth coatings for the military and shielding for sensitive electronics.

In the past few years, the design flexibility of metamaterials — whose properties are determined by their physical structure rather than by their chemical makeup — has been central to their use in the experimental confirmation of the predictions of Victor G. Veselago, who nearly 40 years ago posited that media possessing a negative dielectric constant and permeability would display a negative refractive index. The researchers propose that this ability to control the properties of metamaterials can be similarly exploited to produce the refractive index profile needed to make an object invisible by bending electromagnetic radiation around it.

Pendry explained that the properties of a metamaterial at a given wavelength are determined by its structure at a scale smaller than that wavelength. Consequently, although it is difficult to engineer metamaterials for the control of light, it is much easier to do so for microwaves. He predicted that an experimental demonstration of the material for radar applications would come within a year and a half.

Citing recent successes in the design of metamaterials, Leonhardt also expressed optimism that media to make an object invisible to radar would be experimentally demonstrated in the near-term. He added that nanostructured materials with a custom-designed refractive index at optical wavelengths have been realized and that it is conceivable that the march of scientific progress will lead to further advances.

A potential snag, he noted, is that it seems that the metamaterials must be designed so that the phase velocity exceeds the speed of light — even approaching infinity — in the layers nearest the object to be hidden. This is feasible in principle, but only for a narrow range of wavelengths at a time. He is exploring whether it is possible to escape the need for superluminal propagation and to design a system that would enable broadband invisibility.

Exhibiting the characteristic of materials that are electrical insulators or in which an electric field can be sustained with a minimum dispersion of power. They exhibit nonlinear properties, such as anisotropy of conductivity or polarization, or saturation phenomena.